Method of opening for bags of supple polymeric material subject to interlayer cling

ABSTRACT

Disclosed is a plastic bags that can be easily and reliably opened with a predetermined set of motions. The bags are configured to provide a number of exposed graspable sidewall portions on or near the rim of the bag that can are precisely located so that they can be reliably grasped, manually or by mechanical graspers. These exposed graspable sidewall portions can then be moved in a way that firstly disrupts the interlayer cling, and then secondly holds the bag open for filling. Further steps of automation are possible to seal and remove the bag, and advance the bag.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. patent application Ser. No. 10/450,790 filed Dec. 17, 2001, incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to the art of plastic bags, and in particular to a method of opening bags of supple polymeric material such as is often subject to interlayer cling. The invention also relates to collapsed bags made of supple materials, such as thermoplastic films, which have, integral to their design, features which render them easy to open from the collapsed state so they can be filled with materials. The invention applies to bags of plain (flat) or side-gusseted configurations.

BACKGROUND OF THE INVENTION

Bags made of supple polymeric materials are often difficult to open. It has often been observed that cold welding, static, and various forces and frictions which can collectively be called interlayer cling is a major factor in preventing ready opening of bags from the collapsed state.

Bags are considered ‘difficult’ if they are difficult to open from the collapsed state. The contributors to interlayer cling are many, and range from materials composition, to processing speed, to storage conditions, to time in storage, and even to the inter-individual variation in the stickiness of fingers and also variations in the weather either during manufacture or use. Typical polymeric materials as used to make bags are economical to form into products, because they are thermoplastics of which the softening/melting point, or temperature where properties change markedly, is much closer to the ambient temperature in the factory environments than is the case for, say, metals, glass, paper, cotton, etc. The opposite side of the same coin is that their critical temperatures are equally close to the temperatures of the places where the products will be used; the consequence of that is that nearly anything that can happen in seconds during manufacture can also happen at the ambient temperature; it merely happens more slowly. Many behaviours are thus possible from articles made of such materials, and there is little that can be done to formulations to alter the fact that, whether occasionally or frequently or typically, problems will occur. In other words, no matter how careful a manufacturer is, the problem of ‘difficult’ bags is bound to arise. While a few people know that tricks like rubbing a ‘difficult’ bag between two ripe tomatoes will often cause it to open, and other individuals resort to licking fingers to increase the finger-sidewall coefficient of friction, these approaches are hard on the stock of tomatoes, and also unhygienic.

Many common diseases are transmitted by touching objects and contaminating them, or touching contaminated objects. Any habit involving saliva, such as the finger-licking to which people are driven by ‘difficult’ bags, has a measurable cost in terms of direct expenses in management of patients, indirect costs in terms of lost productivity, and indirect costs in terms of liability when better methods are available. Clearly there is a ready need awaiting a solution to the problem of bags that are difficult to open, and many patents filed by the industry (e.g. CA 916383 to Walsh and Krein, U.S. Pat. No. 4,911,560 to Hoover et al, U.S. Pat. No. 5,611,627 to Belias et al.) have had the objective of rendering bags more easy to open.

Several approaches have been made for paper packets, which are a different Art. Robert Jack, of Rutherglen, Victoria, Australia, filed patent (Nr. 94831, Klasse 54: Papierzeugnisse, 3 Jan. 1897) in Germany for a paper packet (having reveals or tabs to enable a pushing or pulling, perpendicular to the packet plane, of one stiff semi-rigid sidewall (paper is by nature stiff, until it has been creased, which is a starting point toward disintegration as creasing is exercised) relative to the other.

Shakirov (SU001822842A1) repeated some of Jack's teaching, also for paper packets (references to ‘packet’, a word clearly restricted to paper in this context, ‘cemented’ etc. in the Derwent translation clearly place the invention in the Art of paper packets and not the Art of polymeric bags). Again the reveals and tabs enable a pushing or pulling, perpendicular to the packet plane, of one stiff semi-rigid sidewall (again employing the natural stiffness of paper) relative to the other. Further confirming the pushing/pulling nature of the operation in Shakirov is his FIG. 1 showing a packet with noncoincident holes which admit of an action pushing the opposing sidewalls, but do not admit of a lateral pulling in the plane of the packet. There is no evidence to suggest that Shakirov was considering anything but paper packets. Both Jack and Shakirov consist of teachings in a different Art.

The approaches of Jack and Shakirov are suited to a non-supple material, and are both in the Art of paper packets composed of elements that are made of pieces separately cut, reoriented, and ‘cemented’ together, as opposed to plastic bags that are formed as a tube of thermoplastic that is then welded and cut without reorientation. I.e. in the blown-film method by which virtually all such bags are currently made, there is no ‘piecing’ together; only a series of layers formed from a flattened and sometimes folded tube in which all layers are cut or welded as needed, without any reorientation, and generally with cut or weld extending through the entire thickness of the multilayer structure. The skills applicable in the Art of paper packets (where skill components include handling of thermally stable materials, cutting them, orienting parts, cementing or gluing, where glues are applied to the material and set by evaporation more than cooling) is not readily transferable to the Art of polymeric bags (where skill components include transformation of cold solid pellets to a hot fluid to a cooled membrane, where bag panels are welded by heat without the need for glue as such, and where bonds and indeed the material itself become solid only through cooling and can become fluid again by heating as in welding, where cutting operations require care to prevent ‘cold-welding’, etc). In short, paper and thermoplastics are radically different materials and the Arts suitable to one are not readily transferable to the other.

Furthermore, both Jack and Shakirov place their reveals near the centers of their packets' mouths. The amount of movement required to render a flat supple bag open by ‘peeling’ layers apart from a pair of graspable points somewhere along the width of the bag mouth can be algebraically represented. For simplicity, assuming symmetry (lack of which will simply limit the extent of opening possible), consider a flat supple bag having graspable points spaced x units apart and positioned y units from the edge: on tension, the region x will be sheared and then with continued pulling the regions y will be peeled. The total motion required to fully open the bag, i.e. fully disengage the front and rear sidewalls from each other, will be y. Clearly, the highest efficiency for reaching this goal is by minimising y, which Bell does, whereas in contrast neither Jack or Shakirov do that, in fact they seem to maximise y rather than minimise it, which in fact makes sense in a paper packet because the rigidity of the sidewalls enables a separation to propagate rapidly, according to the paper stiffness, so that Jack's and Shakirov's prying action becomes efficient for a paper packet, even though it would not be efficient for a supple polymeric bag.

Those observations at once add confirmation to the difference in the Art addressed by Jack and Shakirov from the Art addressed by Bell, and also show that, even if applied to the latter Art, Jack and Shakirov would be different from Bell (and non-ideal solutions). Paper bags have long had single reveals to facilitate opening by flexing at those reveals and causing one semi-rigid sidewalls to spring away from the other, but that has never been applied to plastic bags, and indeed it would not work, because plastic film is too supple for one layer to spontaneously and reliably spring away from the other in response to such mild flexing. Confirming the difference between the paper and plastics arts, or the lack of direct transferability of the teachings of Jack and Shakirov to plastics, we do not see the Art of Jack or Shakirov applied to plastic bags, despite that Jack dates from more than a century ago, and Shakirov well over a decade. That is traceable to either the information does not travel between the arts, or Jack and Shakirov are not directly applicable.

Better methods of opening bags would clearly improve hygiene, health, workflow, and economy, and therefore they would clearly be useful.

While rubbing requires pressure that often increase interlayer cling in proportion to the force applied and often is a relatively fruitless and frustrating exercise, and taught that in principle if the first and second sidewalls were able to be sheared in opposite directions, doing so would disrupt static cling efficiently, i.e. with very little force required, because the method allows the application of lateral tension without increasing the normal force tending to hold the sidewalls together. Like any large handle adapted for the human hand in order to enable a fine tool to address a very small object, the limitations of the human hand in grasping something as thin as a single layer or sidewall of a bag can be overcome if a suitable ‘handle’ is provided. Such ‘handles’ are provided by creating a bag architecture that left regions at or near the bag mouth where only a single sidewall was present or where it was possible to address one sidewall separately from the other by grasping at one such point. A plurality of such points appropriately situated could then allow the first and second sidewalls to be independently grasped or addressed and tensioned in opposing directions to shear them apart while in tension. This method is efficient because it does not increase the normal forces that amplify the sticking forces collectively known as interlayer cling. A presence of three or more such points can further allow for the bag to be both opened and then for the mouth to held in an open polygonal configuration defined by the positions of the devices which grasp such points.

This approach has been applied to side-gusseted bags.

Whereas human operators rub and rumple bags, and repeat this redundantly until they detect that an opening has occurred, and then change actions to exploit that opening, the detection part of that has been beyond the state of the art for mechanical devices to open bags. In currently known mechanical bagging systems for bags of supple polymeric materials, applications do not include any means by which a machine can detect that the redundant operation has succeeded so that the machine can stop that step and continue with the next step in opening.

Avoiding the difficulty of opening altogether, one kind of automated bagging employs the form-fill-seal approach whereby a bag is formed in place from a sheet (by definition the bag is already open) and then welded closed around the contents. That approach has several disadvantages, particularly that the cycle of filling and forming needs not only to be synchronised, but also to be performed at a steady pace without interruption.

Thus, when considering mechanical opening of bags from a closed or collapsed state, applications are either human-assisted, or fully automatic; in principle limited to systems which fall into either of two groups, the certain-action group and the redundant-action group. Mechanical opening involves either [a] a requirement that either an action must be certain and reliable the first time, and conducted once, or [b] if not reliable the first time the action must be redundantly conducted, i.e. conducted some number of times necessary to result in a near-certainty of effect. Currently, all applications fall into the second group, i.e. the first group has until now no representatives except where humans are involved in a semi-automated system (and even then it could be argued that a redundant-action approach is combined with human sensory capabilities). In a common redundant-operation approach for full automation, bags used are specially made with a front shorter than the back, or the front must be slit open or pre-opened while the back is left intact; then, by holding the bag by the back and blowing compressed air at the top of the front, the front eventually disengages to open the bag. One disadvantage is the constrained architecture of that type of bag.

SUMMARY OF THE INVENTION

The present invention is concerned with making plastic bags that can be easily and reliably opened with a predetermined set of motions. A plastic bag as referred to is generally a collapsed bag of unitary construction, made of supple polymeric material such as is commonly and to some extent unpredictably subject to interlayer cling, comprising first and second opposed contiguous flat sidewalls with joined lateral edges defining left and right sides of the bag; a bag mouth defined by upper edges of said sidewalls. The upper edges of the sidewalls may be straight or otherwise. The sidewalls may have apertures cut through them near the top of the bag to create handles.

The bags are generally rendered easy to open by providing a reliable and definite means of addressing the panels separately from positions where tension when applied can propagate across the bag mouth causing a shearing of the panels against each other as they move, however slightly, in opposite directions and thus releasing the interlayer cling that otherwise impedes opening.

The principle of shearing opposing bag panels against each other, as taught here, can be applied to opening of bags either manually, where the bag is opened and then easily handled by any points around its rim by grasping of course only one sidewall at a time (as to grasp both at once would be counterproductive); or mechanically, where handling requires a mechanism to have already gripped and held key points around the rim so that when the interlayer cling is disrupted these same key points can be reoriented by moving the mechanical devices that have gripped them, resulting in the possibility of a machine holding a bag in virtually any degree of openness.

Key in the manual operation of any bag is eye-hand coordination, and image processing that allows the parts of the bag and the state of openness or closedness at many points around its rim to be instantly evaluated and the hand instructed to exploit the parts that are sufficiently open that a single sidewall can be gripped; this level of intelligence in operation can easily cope with a bag having only one pair of laterally opposed exposed graspable sidewall portions.

That level of sensory and intelligent function is not readily available in machines, so the ability for a machine to handle a ready-made bag is here accomplished by the provision of three or more graspable sidewall portions proximate to the mouth of the bag, whereby firstly interlayer cling can be overcome by grasping and then moving the members of at least one pair of laterally opposed exposed graspable sidewall portions away from each other, and secondly reconfiguring the horizontal shape of the bag mouth by appropriately repositioning at least three exposed graspable sidewall portions.

The present invention allows for a precise-grasping approach, in contrast to the redundant-action approach known in the related art and described above, to mechanical bag handling. That was not possible before because no bag existed that would not require a machine to be precise on the scale of the thickness of a single sidewall of a normal bag of thin gauge. It would be uneconomic to accommodate mechanical use by increasing wall thicknesses to be tractable with the low level of handling precision available. In short, the thickness of the sidewall of any commonly used produce or shopping packaging bag was considerably smaller than the mechanical precision available in a grasping device. In effect, a principle relevant to this invention is that the handling of any item by any handler requires either that they be appropriately matched in scale or that a tool be used to adapt the scale of one to the other. This invention overcomes the disparity in scale, between a single thickness of a plastic bag's sidewall on the one hand and the human hand or mechanical gripper expected to handle it on the other, by creating exposed graspable sidewall portions that are appropriately matched to the scale of a human hand or to the scale of an readily conceivable mechanical gripping device.

The approach followed here allows bags to be made which can be opened by a precisely arranged set of motions (which may vary according to the embodiment). The bags enable this by providing a number of exposed graspable sidewall portions on or near the rim of the bag that can are precisely located so that they can be reliably grasped, manually or by mechanical graspers. These exposed graspable sidewall portions can then be moved in a way that firstly disrupts the interlayer cling, and then secondly holds the bag open for filling. Given this disclosure, further steps of automation are possible to seal and remove the bag, and advance the bag.

The precise-grasping approach can be enabled in side-gusseted bags by making a bag in which a point at each of the four gusset points is graspable. By grasping three or more points, a machine can not only shear front and back panels against each other to disrupt static cling, but can also hold the bag open for filling. Automation can involve feeding of bags from a supply, which can be a roll that delivers bags from below or above.

In flat bags formed from, or like, a flattened tube, the precise-grasping approach can be enabled by providing a plurality of graspable points on the rim of the bag. By grasping three or more points, a machine can not only shear front and back panels against each other to disrupt static cling, but can also hold the bag open for filling. Automation can involve feeding of bags from a supply, which can be a roll that delivers bags from one side.

Flat bags of the die-cut-handle type, familiarly rectangular in shape although other top profiles are possible, where a handle is formed by the creation of an aperture through both front and rear sidewalls of a bag, also often present opening difficulties due to interlayer cling. The principle of shearing via an accessible grip or pressure point available at a scale much larger than the thickness of the layers comprising the bag can be brought to bear by creating a lateral non-coincidence of the two apertures in the front and rear sidewalls.

Other aspects and advantages of embodiments of the invention will be readily apparent to those ordinarily skilled in the art upon a review of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a front perspective view of a bag having exposed graspable sidewall portions at or near the lateral edges near the top of the bag to allow tensioning to open the bag across all of the mouth area between the grasping points;

FIG. 2 shows a series of side-welded bags as formed side-to-side, and the cutouts or voids or weakenings that expose graspable portions of the opposing sidewall;

FIG. 3 shows one embodiment of a mechanically-handleable flat bag in collapsed state (A) and a perspective rendition of opened state (B), in relation to one possible arrangement of mechanical grippers;

FIG. 4 shows another embodiment of a mechanically-handleable flat bag in collapsed state (A) and a perspective rendition of opened state (B), in relation to one possible arrangement of mechanical grippers; and

FIG. 5 shows die-cut handle bags having noncoincident handle apertures that enable easy opening of the bag from the collapsed state.

This invention will now be described in detail with respect to certain specific representative embodiments thereof, the materials, apparatus and process steps being understood as examples that are intended to be illustrative only. In particular, the invention is not intended to be limited to the methods, materials, conditions, process parameters, apparatus and the like specifically recited herein.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Illustrating the application of exposed graspable sidewall portions to a flat bag to be opened manually, FIG. 1 shows a bag 10 having flat first and second sidewalls 16 and 17 with graspable sidewall portions 12 and 13 exposed by voids or weakenings 11 a and 11 b in the opposing sidewalls, such that when the exposed graspable sidewall portions 12 and 13 are grasped and tensioned slightly in directions 14 and 15 respectively, a shearing of the first sidewall 16 occurs in direction 18 opposite to the direction 19 of motion of the second sidewall 17, thus disrupting the interlayer cling that otherwise could render the bag difficult to open.

The placement of the voids 11 a and 11 b near the edges allows a simple action to disrupt interlayer cling across virtually the entire bag width; placement at the extreme edges of the bag has the additional advantage in manufacturing: as bags are being produced in a side-by-side configuration as is common for side-welded bags, in that a single punch or cutting operation creates two voids at once: the (e.g.) left-hand one in the present bag at the same time as the right-hand one in the next following bag. For some purposes manufacturers separate bags as they are side-welded, for other purposes strips of bags are rolled up into or onto rolls, but virtually all side-welded bags originate as bags in a strip of bags. For example, FIG. 2 shows bags 21, 22, 23 having been formed side-to-side in the manner described; the first sidewall 24 and second sidewall 25 are punched alternately at each bag break; following punching, the side-welding and either perforating (if perforated-tear-off rolls of bags are desired) or cutting (if single bags are desired) would occur. The positioning of the voids, to expose graspable sidewall portions, at the extreme edges results in a potential economy by halving the number of punching or cutting operations required.

Applying the principle to a mechanically openable bag with a plurality of exposed graspable sidewall portions on at least one sidewall, FIG. 3-A shows one possible embodiment as a bag 30, having first sidewall 30.1 (shown with dashed line) and second sidewall 30.2 (shown with solid line) with primary voids or reveals 31 a and 35 a (in first and second sidewalls) to expose graspable sidewall portions 31 b and 35 b (in second and first sidewalls), and secondary voids 32 a and 36 a (in second and first sidewalls) to expose graspable sidewall portions 32 b and 36 b (in first and second sidewalls). It can readily be seen that this configuration lends itself to automated or mechanical bag handling: in one possible arrangement for bag 30 one gripper set 33 would address graspable points on the second sidewall, while a second gripper set 34 would address the first sidewall's graspable points. By moving, as in FIG. 3-B, gripper set 34 left, laterally with respect to the other, in direction 37 parallel with the plane of the bag, a shearing motion is executed which will disrupt the interlayer cling. Then, by moving gripper sets apart, for instance moving the gripper set 34 toward us out of the plane of the drawing, the bag mouth is expanded for a filling operation, as depicted in FIG. 3-B.

Showing by way of example that there is an considerable range of possible embodiments for this approach, FIG. 4-A shows another possible embodiment as a bag 40, having first sidewall 40.1 (shown with dashed line) and second sidewall 40.2 (shown with solid line) with voids or reveals 41 a and 42 a (primary and secondary, in first sidewall) to expose graspable sidewall portions 41 b and 42 b (on second sidewall), and voids 45 a and 46 a (primary and secondary, in second sidewall) to expose graspable sidewall portions 45 b and 46 b (in first sidewall). It can readily be seen that this configuration lends itself to automated or mechanical bag handling: in one possible arrangement for bag 40 one gripper set 44 would address graspable points on the second sidewall, while a second gripper set 43 would address the first sidewall's graspable points. By briefly moving one gripper set laterally with respect to the other, a shearing motion is executed which will disrupt the interlayer cling. By then rotating the gripper sets, the bag is held open for a filling operation, as depicted in FIG. 4-B.

A further type of bag in general use is the die-cut-handle bag, a flat bag with a hole or holes that is or are punched through both first and second sidewalls to form a handle, or as a means by which to hang, for example, a newspaper, commercial sample, etc., on a doorknob. In this type of bag as normally executed the problem of interlayer cling is often a nuisance. An opportunity exists to ease opening by changing the apertures or handle holes so that the apertures on the first and second sidewalls are noncoincident with each other. That enables a simple finger motion to tension the sidewall areas surrounding the apertures, but apply the tension oppositely to each of the two sidewalls so that they will tend to shear against each other. FIG. 5-A shows a bag 50 with apertures that coincide as an area 51 but leave areas 52 and 53 as single layers of either the first or second sidewall, respectively. FIG. 5-B shows the same bag 50 after an outward force or distortion 55 has been applied as indicated by the arrows to the regions of noncoincident aperture and thereby caused a disengagement of the sidewalls in the regions above and below the complete aperture and in the top 54 region of the bag. To illustrate that the concept is not restricted to bags with a straight trimmed top, FIG. 5-C shows a bag 60 with a complete aperture 61 and areas 62 and 63 as single layers of either the first or second sidewall, respectively, enabling the same process of expanding by fingers, in a natural motion similar to picking up the bag by its handle, the complete aperture and causing a shearing of the surrounding areas of sidewalls against each other, releasing interlayer cling and rendering the bag open.

Numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. 

1. A collapsed bag of unitary construction made of supple polymeric material that can create interlayer cling, comprising: first and second opposed contiguous flat sidewalls, each having an upper edge and a pair of lateral edges, said first and second sidewalls being joined together at their respective lateral edges to define left and right sides of the bag, said first and second opposed contiguous flat sidewalls being subject to interlayer cling; and a bag mouth defined by the upper edges of said sidewalls, the upper edges being continuously coincident along a major and central portion thereof; said first sidewall having a first void or weakening of a portion at or near the lateral edge thereof on the right side of the bag and in the vicinity of the bag mouth, the first void or weaking extending partially down the right lateral edge and extending inwards along the upper edge, terminating at a point before the center of the bag; said second sidewall having a second void or weakening of a portion at or near the lateral edge thereof on the left side of the bag and in the vicinity of the bag mouth, the second void or weaking extending partially down the left lateral edge and extending inwards along the upper edge, terminating at a point before the center of the bag; and said first and second voids or weakened portions exposing respective graspable sidewall portions in the opposing sidewall in a diagonally opposed relationship, whereby applying a lateral tension to said exposed graspable sidewall portions introduces a shearing action between said first and second opposed contiguous flat sidewalls to break said interlayer cling and open the bag mouth.
 2. A collapsed bag of unitary construction made of supple polymeric material that can create interlayer cling, comprising: first and second opposed contiguous flat sidewalls, each having an upper edge and a pair of lateral edges, said first and second sidewalls being joined together at their respective lateral edges to define left and right sides of the bag, said first and second opposed contiguous flat sidewalls being subject to interlayer cling; and a bag mouth defined by the upper edges of said sidewalls; said first sidewall having a primary void or weakening of a portion at or near the lateral edge thereof on the right side of the bag and in the vicinity of the bag mouth; said second sidewall having a similar primary void or weakening of a portion at or near the lateral edge thereof on the left side of the bag and in the vicinity of the bag mouth; said primary voids or weakened portions exposing respective graspable sidewall portions in the opposing sidewall in a diagonally opposed relationship; said first and second sidewalls each having also at least one secondary void or weakening each exposing a respective graspable sidewall portion in the opposing sidewall; wherein a plurality of exposed graspable sidewall portions thus exist for each sidewall; whereby an appropriate series of steps of grasping and moving said exposed graspable sidewall portions can cause interlayer cling to be disrupted and the bag to be held in an open state ready for filling.
 3. A collapsed bag of unitary construction made of supple polymeric material that can create interlayer cling, comprising: first and second opposed contiguous flat sidewalls, each having an upper edge and a pair of lateral edges, said first and second sidewalls being joined together at their respective lateral edges to define left and right sides of the bag, said first and second opposed contiguous flat sidewalls being subject to interlayer cling; and a bag mouth defined by the upper edges of said sidewalls; said first sidewall having in the vicinity of the bag mouth one or more apertures; said second sidewall having in the vicinity of the bag mouth one or more apertures of which one or more is partially non-coincident with one or more the apertures of the first sidewall; wherein the areas covered by both sidewalls' apertures forms a complete aperture and the areas covered by only one sidewall's aperture form an incomplete aperture or a single-sidewall region, and other parts of the bag as two-sidewall regions; whereby a lateral outward force on the single-sidewall regions at the outer edges of the complete apertures can cause the sidewalls that are in regions near the apertures to come under tension against each other and shear in opposite directions, thus rendering the bag open in the region of the apertures.
 4. A method of opening a collapsed bag of claim 1, the method comprising: grasping said exposed graspable sidewall portions independently at said exposed graspable sidewall portion; tensioning said exposed graspable sidewall portions to introduce a shearing action between said first and second opposed contiguous flat sidewalls over substantially the full width between said exposed graspable sidewall; and laterally displacing said sidewalls relative to each other by a movement that may be relatively small, over substantially the full width between said exposed graspable portions.
 5. A method of opening a collapsed bag of claim 2, the method comprising: grasping said exposed graspable sidewall portions independently at said exposed graspable sidewall portion; tensioning said exposed graspable sidewall portions to introduce a shearing action between said first and second opposed contiguous flat sidewalls over substantially the full width between said exposed graspable sidewall; and laterally displacing said sidewalls relative to each other by a movement that may be relatively small, over substantially the full width between said exposed graspable portions.
 6. A method as claimed in claim 5, followed by the step of positioning the exposed graspable sidewall portions so as to hold the bag in an open state.
 7. A method as claimed in claim 5, wherein the method is carried out by mechanically operated graspers.
 8. A method as claimed in claim 6, where the method is carried out by mechanically operated graspers.
 9. A method of opening a collapsed bag of claim 3, the method comprising fingers or instruments applying an outward force, which may be small, to the incomplete aperture areas at the edge of the complete aperture, thereby causing opposing tension to be developed between the first and second sidewalls in the region surrounding the aperture or apertures, leading to an opening of the bag.
 10. A collapsed bag as claimed in claim 1, further comprising a pair of opposed side gussets located between said first and second opposed contiguous sidewalls, each said gusset having first and second gusset panels hingedly joined to respective side edges of said first and second sidewalls, said gusset panels being freely displaceable and deformable relative to said sidewalls; wherein each graspable sidewall portion is narrower than the width of said pair of opposed side gussets.
 11. The bag of claim 3, in which the lateral edges of the bag are infolded to form side gussets.
 12. The bag of claim 3, in which the bottom of the bag is infolded to form a bottom gusset.
 13. A collapsed bag of unitary construction made of supple polymeric material that can create interlayer cling, comprising: first and second opposed contiguous flat sidewalls, each having an upper edge and a pair of lateral edges, said first and second sidewalls being joined together at their respective lateral edges to define left and right sides of the bag, said first and second opposed contiguous flat sidewalls being subject to interlayer cling; and a bag mouth defined by the upper edges of said sidewalls, the upper edges being continuously coincident along a major and central portion thereof; said first sidewall having a first void or weakening of a portion at or near the lateral edge thereof on the right side of the bag and in the vicinity of the bag mouth; said second sidewall having a second void or weakening of a portion at or near the lateral edge thereof on the left side of the bag and in the vicinity of the bag mouth; and said first and second voids or weakened portions exposing respective graspable sidewall portions in the opposing sidewall in a diagonally opposed relationship, whereby applying a lateral tension to said exposed graspable sidewall portions introduces a shearing action between said first and second opposed contiguous flat sidewalls to break said interlayer cling and open the bag mouth.
 14. A collapsed bag according to claim 13, in which said first and second voids or weakenings intersect the right lateral edge of the bag
 15. A collapsed bag according to claim 13, in which said said first and second voids or weakenings intersect the top edge of the bag
 16. A collapsed bag according to claim 13, in which said said first and second voids or weakenings intersect the right lateral edge of the bag and intersect the top edge of the bag 